(222e) Effect of Functionalization on Surfactant Activity of Amphipathic Surfactants – Physics of Bile Salts and Counter-Ions in Aqueous Suspensions of Single-Walled Carbon Nanotubes

Authors: 
Khare, K. S., National Institute of Standards and Technology
Phelan, F. R. Jr., National Institute of Standards and Technology
Bile Salts constitute a diverse class of multifunctional amphipathic surfactants. Recently, bile salts have been employed in analytical centrifugation (AUC) to efficiently enrich and separate single-walled carbon nanotubes (SWCNT) based on chirality. Thus, bile salts seem capable of amplifying the relatively minor differences in hydrodynamic behavior of SWCNTs based on chirality. Further, it was found that subtle single-point mutation of functional groups on bile salts had a drastic impact on the hydrodynamic behavior of the aqueous suspensions of SWCNTs. These results provide strong motivation for understanding the relationship between molecular architecture and thermodynamics of the bile salts at the aqueous SWCNT interface. We use all-atom molecular dynamics simulations to study models of SWCNT systems containing different bile salts. Our findings indicate that the overall hydrodynamic behavior of the SWCNT-surfactant complex in water is influenced by an interplay of interactions between (a) SWCNTs and surfactants, (b) surfactants between themselves, (c) surfactant and the counter-ion, and (d) the counter-ion and its hydration layer.